Wireless Crane Scale Range: How Far the Reading Travels — and What Blocks It
Steel is a wonderful conductor and a terrible neighbour for radio.
That one line explains most of what goes wrong with wireless crane scale range. On paper, a 2.4 GHz radio could reach the far end of a kilometre-long yard. Inside a steel shed it can struggle to reach the desk at the end of the bay. Nothing is broken. This article covers how far the reading really travels, what steel, people and rain do to it, why a confirmed reading beats a repeated one, and where to put the receiver — from the published standards and from how Hindustan Scale Company (HSCo) builds its Bluetooth crane scales.
Why the reading has to leave the hook at all
Because nobody should be under the load to read it.
The US crane standard (29 CFR 1926.1425) bars everyone from the fall zone of a suspended load except those hooking, unhooking or guiding it; 29 CFR 1910.179 tells the operator to avoid carrying loads over people; India’s crane-safety code, IS 13367 (Part 1), says all persons should stand clear of the load being lifted.
A crane scale’s display hangs from the hook, above the load, facing whoever walks underneath. The radio exists so that nobody has to. The weight goes to a phone, a handheld remote or a desk indicator across the bay. Range is a safety distance.
Range is a property of the whole link, not a number on the box
The Bluetooth SIG, which writes the standard, puts it plainly: effective range runs from under a metre to over a kilometre, set by transmit power, antenna, receiver sensitivity and the path in between.
The band is the same free band Wi-Fi and phones use, 2.4 GHz — licence-free, but capped and shared. Europe caps radiated power at 20 dBm, one-tenth of a watt (ETSI EN 300 328). India’s 2005 rules (G.S.R. 45(E) of 28/01/2005) allow up to 1 W at the transmitter and 4 W radiated, with no licence, on a “non-interference, non-protection and shared” basis. Shared means your crane scale, the plant Wi-Fi and every phone in the building talk on the same air.
By the ITU’s free-space formula, a 2.45 GHz signal loses about 60 dB over 10 m, 80 dB over 100 m and 100 dB over 1 km; each doubling of distance costs only 6 dB. A full-power transmitter and a receiver at the weakest sensitivity the Bluetooth specification permits give a budget that, on paper, stretches to roughly a kilometre — a generic illustration, not a figure for any product, but it makes the point. When the reading dies at 30 m, the radio has not run out. The building has spent the budget.
What is a realistic wireless crane scale range inside a steel shed?
A US government laboratory, NIST, measured inside real factories how fast a 2.2 GHz signal fades with distance. In open air it lost 5.4 dB every time the distance doubled — the free-space figure. In a machine shop, 5.7 dB. In a steam plant, 8.1 dB. Inside an automotive transmission plant, 12.9 to 17.8 dB per doubling — two to three times the open-air rate. The ITU’s indoor model (P.1238) adds the nuance: with a clear sight line an industrial hall behaves close to free space. Obstruction is what steepens the loss.
Put the two together and a rule-of-thumb ladder falls out. Every figure is indicative — the assumptions are ours (a modest radio, a typical receiver, a generous margin for the echoes NIST measured) — and none of it is a product specification.
| Situation in the bay | Indicative reach — rule of thumb derived from the ITU and NIST models |
|---|---|
| Modest radio, clear sight line, machine-filled plant | about 40–55 m (NIST plant fits); about 70 m (ITU industrial model) |
| The same, with one person standing in the path | about 15–25 m |
| One person plus a steel column or machine shadowing the path | about 5–15 m |
| Full-power radio, clear sight line, machine-dense plant | roughly 90–120 m |
The lower rungs land near the 10 m that HSCo publishes for the handheld remote of its CRHBT5K Bluetooth crane scale — a modest figure, and an honest one. The phone link is best described the same way, a few metres to tens of metres depending on the bay, and the desk indicator of a two-box system is a separate receiver whose reach HSCo quotes per site, after a walk of the bay.
Steel throws the radio back, and the echo is what corrupts the reading
By the ITU’s table of building materials (P.2040), metal conducts electricity roughly a hundred million times better than concrete. A 2.4 GHz wave gets about three microns into steel before it is thrown back: a steel sheet is a mirror, not a window. A steel column shadows the link; a steel-clad shed bounces the signal from wall to wall; a row of steel-clad machines forms what NIST’s deployment guide calls a “canyon”, inside which a radio is unreliable.
The guide’s sharper point: reverberation, not weak power, is the enemy. In a reflective shed the power arriving is barely reduced, but it arrives spread out in time, as a string of echoes, and that “can cause significant distortions and result in data loss and delay”. A reading corrupted by its own echo has to be sent again.
Line of sight also means more than seeing the hook. By the ITU’s own rule (P.530), the signal wants a clear football-shaped zone around the straight line — about 0.55 m either side at mid-path for a 10 m link, 0.8 m for 20 m, 1.2 m for 50 m — with at least 60 % of it kept clear. That is why a column a metre off the sight line still matters. NIST applies the same rule of thumb to factories, adds that indoors full clearance is rarely the root cause on its own, and insists instead on placement: antennas high, above the machinery, in clear view of the other device, never near the floor.
Rain does not block the link. Wet things and people do
By the ITU’s rain model (P.838), a 2.4 GHz signal loses a few hundredths of a decibel per kilometre even in a 100 mm/h cloudburst — a couple of thousandths across a 50 m bay. It is one model’s figure, but rain in the air costs nothing measurable at this frequency.
What hurts is water on things, and bodies. A peer-reviewed 2018 study in Sensors measured one person standing in the path of a 2.4 GHz link: about 10 dB lost, and 10 to 20 dB with the body against the unit. Ten decibels is roughly the same as trebling the distance in open air. Wet ground has ten times the permittivity of dry by the ITU’s material table, and NIST’s guide lists liquids and fog as significant absorbers. The operator’s own body between hook and phone, a soaked tarpaulin and a closed steel shed in the monsoon all change a link that rain itself does not.
Why sending more often makes it worse — and a confirmation makes it better
When a reading goes missing, the instinct is to transmit more often. On a shared band that is wrong.
Every data packet in a standard Bluetooth connection is acknowledged; a packet that arrives damaged is simply not acknowledged, and the sender resends it. That is the Bluetooth Core Specification’s own mechanism, and blind repetition works against it. Kleinrock and Tobagi’s classic 1975 analysis showed that a channel where radios transmit whenever they please tops out at 18 % useful use (37 % with time slots) and collapses towards zero when overloaded — which is why “send more often” fails once several radios share a bay. Regulators forbid it anyway: under ETSI EN 300 328 a non-adaptive full-power 2.4 GHz radio may occupy the air at most 10 % of the time.
Legal metrology asks the same from the other side: OIML D 31:2023 requires transmitted measurement data to be checked and, if damaged, discarded — and a slow or broken link must lose no reading. HSCo builds its wireless weighing links on that principle: a reading is confirmed, not just repeated. A link that shouts louder is not a link that is heard better.
What a longer range is not
Not a licence question. The band is licence-free in India under the 2005 rules.
Not fixed by more power. Regulators cap it, and the arithmetic is unkind: 3 dB more buys about 40 % more distance in open air and barely a tenth to a sixth more inside a machine-dense plant.
Not a replacement for the stamped display. The verified display on the scale remains the legal weight; the phone, remote and indicator show a faithful copy.
Not a number on a box. No range survives every building; the honest answer is a ladder and a walk of the bay.
What changes on Monday morning
- Nobody stands under the load to read it. The weight comes to the phone, the remote or the desk.
- A late reading has a known cause — the body, the column, the shed — not a mystery fault in the scale.
- Receiver placement becomes a five-minute decision: high, above the machinery, in sight of the hook.
- The reading you act on is a confirmed one. Not the last of several hopeful repeats.
How to start: one bay, thirty days
- Pick one crane and one bay — the one where the operator walks furthest to read the hook.
- Walk it with the receiver. With the crane at the far end, mark where the reading holds — then again with someone standing in the path.
- Mount the receiver high, above machinery, in clear sight of the hook and away from rows of steel-clad machines.
- Keep the reader out of the path — beside the line between hook and receiver, not on it.
- Measure for thirty days: readings held, readings late, minutes spent walking under loads. Extend only when the numbers justify it.
Hindustan Scale Company has made weighing scales in Mumbai since 1955. Its CRHBT Bluetooth crane scales run from 3 t to 50 t; the 5,000 kg CRHBT5K sends its weight to the HSCo Android app, has a handheld remote for tare and zero (published range up to 10 m), a jumbo remote or Wi-Fi display option, up to 40 hours on a charge and a Legal Metrology stamp. Indicative prices before GST, September 2026: ₹17,500 (3 t), ₹22,500 (5 t), ₹68,500 (50 t). See the crane scale range, IoT connected weighing scales and the crane scale buying guide.
Frequently asked questions
How far does a wireless crane scale transmit?
It depends on the building more than the radio. In open air a 2.4 GHz link could on paper reach hundreds of metres; inside a machine-filled steel shed a rule-of-thumb ladder derived from the ITU and NIST models runs from roughly 40–70 m with a clear sight line down to 5–15 m with a person and a steel column in the path. HSCo publishes 10 m for the CRHBT5K’s handheld remote and quotes the desk-indicator reach per site.
Does rain reduce wireless crane scale range?
Rain in the air does not: by the ITU’s rain model, 2.4 GHz loses only hundredths of a decibel per kilometre even in a cloudburst. What changes in wet weather is everything else — wet surfaces, soaked tarpaulins, wet ground and a closed steel shed all reflect or absorb the signal.
Why does the reading drop when someone walks across the bay?
A human body in the path of a 2.4 GHz link costs about 10 dB, roughly the same as trebling the distance in open air, and 10–20 dB if the body is pressed against the unit. Keep the reader beside the line between hook and receiver, not on it, and mount the receiver high enough that people cannot stand in the path.
Where should the receiver of a wireless crane scale be placed?
High, above the machinery, with a clear sight line to the hook, and never near the floor — the placement rules NIST gives for factory radio. Keep it out of rows of steel-clad machines, which form a radio “canyon”, and walk the bay with it before fixing it in place.
Do I need a licence to use a Bluetooth crane scale in India?
No. The 2.4 GHz band has been licence-exempt in India since the 2005 rules, on a non-interference, non-protection and shared basis, within the power limits those rules set. The same band carries Wi-Fi and phones, which is why the air is shared.
Is the weight on the phone the legal weight?
The verified, stamped display on the scale remains the legal weight. The phone, the handheld remote and the desk indicator show a faithful copy of it, and OIML D 31 requires that a damaged transmitted reading be discarded rather than shown.
Next step
Tell us the length of your longest bay and what it is clad in, and we will propose a thirty-day trial of one Bluetooth crane scale with the receiver placed where the reading holds.
Hindustan Scale Company (HSCo) · Mumbai · est. 1955 · www.hindustanscale.com · hsc@hindustanscale.com
Sources
- ITU-R Recommendation P.525-5 (11/2024) — Calculation of free-space attenuation, equation (6); ITU-R P.530-19 (09/2025) — Propagation data and prediction methods required for the design of terrestrial line-of-sight systems, sections 2.2.1–2.2.2 (first Fresnel zone, 60 % clearance).
- ITU-R Recommendation P.838-3 (03/2005) — Specific attenuation model for rain for use in prediction methods, coefficients at 2 and 2.5 GHz.
- ITU-R Recommendation P.2040-4 (09/2025) — Effects of building materials and structures on radiowave propagation above about 100 MHz, Table 3; ITU-R P.1238-13 (09/2025) — Propagation data and prediction methods for the planning of indoor radiocommunication systems, Table 2 and the section on body effects.
- NIST Technical Note 1951 (January 2017) — Industrial Wireless Systems: Radio Propagation Measurements, Table 4.1 and section 4.4; NIST Advanced Manufacturing Series 300-4 (April 2018) — Guide to Industrial Wireless Systems Deployments, chapters 2, 5 and 7.
- Tanghe E. et al. — “The industrial indoor channel: large-scale and temporal fading at 900, 2400, and 5200 MHz”, IEEE Transactions on Wireless Communications 7(7) (2008); Januszkiewicz L. — “Analysis of Human Body Shadowing Effect on Wireless Sensor Networks Operating in the 2.4 GHz Band”, Sensors 18(10):3412 (2018).
- Kleinrock L., Tobagi F. A. — “Packet Switching in Radio Channels: Part I”, IEEE Transactions on Communications COM-23(12) (December 1975), Table I.
- Bluetooth SIG — Understanding Bluetooth Range; Bluetooth Core Specification, Vol 6 Part B (Link Layer), section 4.5.9 Acknowledgment and flow control.
- ETSI EN 300 328 V2.2.2 (2019-07) — Wideband transmission systems; data transmission equipment operating in the 2,4 GHz band, clauses 4.3.1.2.3, 4.3.1.6 and 4.3.1.7.
- Government of India — Gazette notification G.S.R. 45(E) of 28/01/2005, Use of low power equipment in the frequency band 2.4 GHz to 2.4835 GHz (Exemption from Licensing Requirement) Rules, 2005; US FCC 47 CFR 15.247.
- OIML D 31:2023 — General requirements for software-controlled measuring instruments, clauses 6.3.5.3 and 6.3.5.4.
- US OSHA — 29 CFR 1926.1425 Keeping clear of the load and 29 CFR 1910.179(n)(3)(vi); Bureau of Indian Standards — IS 13367 (Part 1):1992, clause 13.3.
- Hindustan Scale Company — CRHBT5K Electronic Bluetooth Crane Scale product page (read 14/09/2026); indicative list prices, September 2026, before GST.